The present invention relates to a mechanism for moving an element in opposite directions, and in particular the present invention relates to a hydraulic mechanism for reciprocating an element.
Many kinds of devices require motion of an element in first one direction, and then in the opposite direction. For example, in harvesting equipment a cutter bar reciprocates in opposite directions relative to a fixed comb. Also beds for agitating harvested crops are driven in opposite directions.
Various mechanisms including hydraulic mechanisms have been used in the past to reciprocate such elements. One such hydraulic mechanism is described in U.S. Pat. No. 4,280,396. In this mechanism, a piston moves first in one direction and then in the opposite direction as hydraulic fluid is applied alternately to opposite sides of the piston. The flow of hydraulic fluid is controlled by a spool valve which shifts position when the piston reaches one end or the other of its stroke. As the piston approaches an end of its stroke, the piston uncovers a port which allows the fluid pushing on one side of the piston to be communicated to one end of the spool valve to shift the spool valve. The spool valve then reverses the flow of fluid to the other side of the piston.
The mechanism disclosed in U.S. Pat. No. 4,280,396 has an inherent delay in its operation because fluid starts to shift the spool valve when the piston has reached the end of its stroke. Moreover, some time is required for the spool itself to move. In addition, this mechanism requires a special piston construction with lands and grooves to regulate the flow of fluid to the spool valve.